1. Technical Background
The present invention relates generally to medical devices, and more particularly to a balloon catheter and stent delivery system.
2. Discussion
Balloon catheters are used in a variety of therapeutic applications, including intravascular catheters for procedures such as angioplasty. Nearly one million angioplasties were performed worldwide in 1997 to treat vascular disease, including coronary, neurological and peripheral blood vessels partially or totally blocked or narrowed by a stenosis. By way of example, the present invention will be described in relation to coronary and peripheral angioplasty treatments. However, it should be understood that the present invention relates to any balloon catheter and stent delivery system having enhanced stent retention, and is not limited to angioplasty.
Most balloon catheters have a relatively long and flexible tubular shaft defining one or more passages or lumens, and an inflatable balloon attached near one end of the shaft. This end of the catheter where the balloon is located is customarily referred to as the "distal" end, while the other end is called the "proximal" end. The balloon is connected to one of the lumens extending through the shaft for the purpose of selectively inflating and deflating the balloon. The other end of this inflation lumen leads to a hub coupling at the other end for connecting the shaft lumens to various equipment. Examples of this type of balloon catheter are shown in U.S. Pat. No. 5,304,197, entitled "Balloons For Medical Devices And Fabrication Thereof," issued to Pinchuk et al. on Apr. 19, 1994, and also in U.S. Pat. No. 5,370,615, entitled "Balloons Catheter For Angioplasty," issued to Johnson on Dec. 6, 1994.
A common treatment method for using such a balloon catheter is to advance the catheter into the body of a patient, by directing the catheter distal end percutaneously through an incision and along a body passage until the balloon is located within the desired site. The term "desired site" refers to the location in the patient's body currently selected for treatment by a health care professional. After the balloon is disposed within the desired site, it can be selectively inflated to press outward on the body passage at relatively high pressure to a relatively constant diameter, in the case of an inelastic or non-compliant balloon material.
This outward pressing of a constriction or narrowing at the desired site in a body passage is intended to partially or completely re-open or dilate that body passageway or lumen, increasing its inner diameter or cross-sectional area. In the case of a blood vessel, this procedure is referred to as angioplasty. The objective of this procedure is to increase the inner diameter or cross-sectional area of the vessel passage or lumen through which blood flows, to encourage greater blood flow through the newly expanded vessel. The narrowing of the body passageway lumen is called a lesion or stenosis, and may be formed of hard plaque or viscous thrombus.
Unfortunately, within approximately six months after angioplasty, the lumen at the angioplasty site may re-close or become narrow again. This phenomenon is called restenosis, and may occur in as many as 30-40% of percutaneous transluminal angioplasty patients. Restenosis may require an additional procedure, such as another angioplasty, drug therapy treatment, or even surgery including bypass graft. It is of course desirable to prevent or limit the occurrence of restenosis, especially since some patients may not be preferred candidates for another interventional treatment.
In an effort to prevent restenosis, short flexible cylinders or scaffolds made of metal or polymers, referred to as a stent, may be permanently implanted into the vessel to hold the lumen open, to reinforce the vessel wall and improve blood flow. The presence of a stent tends to keep the blood vessel open longer, but their use may be limited by various factors, including size and location of the blood vessel, a complicated or tortuous vessel pathway, etc. Also, even a vessel with a stent may eventually develop restenosis.
Some stents are expanded to the proper size by inflating a balloon catheter, referred to as "balloon-expandable" stents, while others are designed to elastically resist compression in a "self-expanding" manner. Both balloon-expandable stents and self-expanding stents are generally crimped or compressed to a diameter during delivery that is smaller than the eventual deployed diameter at the desired site. When positioned at the desired site within the lesion, they are deployed by inflating a balloon or being allowed to self-expand into the desired diameter.
Friction forces may tend to cause a crimped stent to slip in a proximal direction while the catheter system is advanced, or to slip in a distal direction if the physician decides to withdraw the stent without deploying it. It is of course desirable to retain the stent in the proper position, during advancement along a vascular path to the desired site.
Accordingly, it is an object of the present invention to provide balloon catheter systems for enhanced stent position retention during longitudinal movement of the catheter.
It is a further object of the present invention to provide methods for making balloon catheter systems having enhanced stent position retention.
These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings.